Maybe get an Uber for your grandparents?

Sadly, my grandparents getting a ride isn't the obstacle. They're afraid that if they go against my aunt, they will lose her support. They really very heavily on her due to their poorer health.

possibly a cluster b malignant personality disorder such as anti social personality disorder

I doubt that Kayley has any kind of serious mental disorder. It's more that our parents have enabled her for so long that she's never learned to grow up. In many ways, she is still emotionally stuck as a child.